On the Evolution of Tropopause Layer Cooling Over Tropical Cyclone

This study investigates the evolution of tropopause layer cooling (TLC) in an idealized tropical cyclone (TC) as well as the physical mechanism for its formation throughout its lifetime. TLC development is closely related to the intensity change of the TC. The TLC within the inner core of a TC coincides with the occurrence of the TC warm core, whereas the enhancement of the TLC precedes the strengthening of the warm core and the intensification of the TC. This phenomenon suggests that the TLC could be a valuable signal for predicting TC intensity and intensity change. After the onset of rapid intensification, the TLC continues to enhance until it is replaced by the warm core in the inner core region, and it expands to the outer core area and forms a cold ring above the TC outflow layer. The budget analyses of the azimuthal mean potential temperature indicate that advection plays a leading role during all stages of the TLC evolution. Prior to and during the rapid intensification stages of a TC, advection (due to eddy motion) contributes to a cooling of the upper layer above the TC center. This upper-level cooling is assumed to be related to the uplift caused by overshooting and convection within the inner core. However, the advection process caused by the azimuthal vertical motion dominated the broad cooling across the whole TLC area.